Soot particles from diesel exhaust can enter arteries and cause them to harden, helping clots to form, which can lead to heart attacks. The findings have potential implications for EPA regulations. However, because the study was so tightly controlled, further research will have to be done to establish causality.
"Diesel exhaust consists of a complex mixture of particles and gases," said study author Dr. Nick Mills, a clinical research fellow at the Edinburgh center. "Before we can advocate the widespread use of particle traps in diesel engines, we need to verify that combustion-derived particles are the responsible component."
study from Edinburgh University, diesel exhaust has been correlated to heart attacks.

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Diesel Exhaust Chokes Human Arteries